Self-written DVD+Rs that cannot be read...

[Hugo van der Merwe <hugo@dsp.sun.ac.za>]

I'm new to DVD writing. I've now got about 15 badly written DVDs. 
growisofs does not give any bad-looking output, everything looks great, 
but the DVDs all have some files that cannot be read. These kinds of 
errors appear in dmesg when trying to read the DVDs I've written:

Buffer I/O error on device hdc, logical block 226047
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x54
ide: failed opcode was 100
end_request: I/O error, dev hdc, sector 904192
Buffer I/O error on device hdc, logical block 226048
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x54
ide: failed opcode was 100
end_request: I/O error, dev hdc, sector 904196
Buffer I/O error on device hdc, logical block 226049
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x54
ide: failed opcode was 100

I miss the output of cdrecord telling me about possible buffer underruns
and the like. ("Burn-free was used 3 times" etc.) What can I do? I've
tried giving the -speed=1 parameter, it still writes at about 4x. I am
using Verbatim DVD+Rs, I suppose I should try something else. What else
is "good quality"? Might Verbatim DVD-Rs work better? Or should I be 
trying a different drive? (Or install Windows to try other software - 
might that help at all, or is this purely a hardware problem?)

Thanks,
Hugo